JP2003321711A - Method of producing gear obtained by using steel for carburization having excellent grain size property as stock - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing a gear with a case hardening steel stock by which the characteristics of case hardening steel can exceedingly be exhibited, and the occurrence of duplex grains can be prevented on carburization after its working into a gear. <P>SOLUTION: In the method of producing a gear having excellent austenite grain size properties on carburization, a bloom or an ingot having a composition containing, by mass, 0.10 to 0.25% C, 0.03 to 0.35% Si, ≤2.0% Mn, 0.15 to 2.00% Cr, 0.0005 to 0.005% B, 0.08 to 0.2% Ti, ≤0.015% N and 0.005 to 0.05% Al, and the balance Fe with inevitable impurities is subjected to thermal history in a series of working stages into a gear including heating to ≥1,200°C, desirably to ≥1,250°C, slab rolling, air cooling, heating at 800 to 1,050°C, bar steel wire rod rolling, and hot forging, the reheating to a temperature range of 800 to 1,050°C is characterized. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a gear, which is made of case-hardening boron steel and has excellent austenite grain size characteristics during carburization.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Application Laid-Open No. 10-130777, Si and Mn are reduced to improve cold workability.
A case-hardening steel for cold working has been invented in which B is added in order to compensate for the deterioration of the hardenability due to the reduction of Si and Mn and Ti is added in order to further improve the grain size characteristics. However, when the steel type is applied to a gear manufactured in the process of hot forging that does not include normalizing after cold forging-cold forging (toothing), Ti carbide during hot forging, a composite carbide containing Ti, Ti nitride grows, it becomes impossible to suppress coarsening of the austenite grain size during carburization, and mixed grains occur in the portion where strain is generated by cold forging, resulting in heat treatment strain.
In order to maintain good grain size characteristics even in this step, Ti carbide, Ti-containing composite carbide, T
It is necessary to suppress the growth of i-nitride.

[0003]

SUMMARY OF THE INVENTION The present invention is a hot forging-
The object of the present invention is to provide a gear manufacturing method for making the most of the properties of case-hardening boron steel in the process of cold forging. That is, it is to provide a gear manufacturing method of a case-hardening boron steel material having excellent grain size characteristics during carburization after gear processing.

[0004]

The means of the present invention for solving the above-mentioned problems is, in the invention of claim 1, mass%.
C: 0.10 to 0.25%, Si: 0.03 to 0.
35%, Mn: 2.0% or less, Cr: 0.15 to 2.0
0%, B: 0.0005 to 0.005%, Ti: 0.0
8 to 0.2%, N: 0.015% or less, Al: 0.00
A bloom or steel ingot containing 5 to 0.05% with the balance Fe and unavoidable impurities at 1200 ° C, preferably 1
After heating to 250 ℃ or more, rolling billets and air cooling, 800 ~
After heating to 1050 ° C, rolling the steel bar wire rod, and further in the heat history of the process of processing into a series of gears including hot forging, 80
It is a method for producing a gear having excellent austenite grain size characteristics during carburization, which comprises reheating to a temperature range of 0 to 1050 ° C.

According to the second aspect of the present invention, C: 0.
10 to 0.25%, Si: 0.03 to 0.35%, M
n: 2.0% or less, Cr: 0.15 to 2.00%, B:
0.0005-0.005%, Ti: 0.08-0.2
%, N: 0.015% or less, Al: 0.005-0.0
Bloom or steel ingot containing 5% and Mo: 0.03 to 1.0% and the balance Fe and unavoidable impurities
After heating to 200 ° C., preferably 1250 ° C. or higher, rolling steel pieces and air-cooling, heating to 800 to 1050 ° C., rolling steel bar wire rods, and further in the heat history of a series of processing steps into gears including hot forging, It is a method for producing a gear having excellent austenite grain size characteristics during carburization, which is characterized by reheating to a temperature range of 800 to 1050 ° C.

The present invention uses the case-hardening boron steel as a raw material as described above, Ti carbide, Ti-containing composite carbide, T
The present invention relates to a method for manufacturing a gear in which coarsening of austenite grain size during carburization is suppressed by finely depositing i-nitride, and mixed grains are not generated. After rolling-air cooling,
After being heated to 800 to 1050 ° C., it is rolled into a steel bar wire rod, and then reheated to a temperature range of 800 to 1050 ° C. in the heat history of a series of gear forming processes including hot forging.

The reasons for limiting the composition ratio of steel in the present invention will be described. The following shows mass%.

C: C is an element necessary for securing the strength of the core portion after carburizing as a machine structural part, and is 0.1
If it is less than 0%, the effect cannot be sufficiently obtained, and conversely 0.2
If it exceeds 5%, the toughness of the core part is lowered. Therefore, the content is set to 0.10 to 0.25%.

Si: If Si is less than 0.03%, a sufficient deoxidizing effect cannot be obtained, and if it is contained excessively, the workability is deteriorated and the formation of an intergranular oxide layer during carburization is promoted, and the fatigue property is also deteriorated. Therefore, the upper limit was made 0.35%.

Mn: Mn is an element necessary to secure hardenability, but if it exceeds 2.0%, workability is deteriorated. Therefore, the content is set to 2.0% or less.

B: B is an element that significantly improves the hardenability of steel by the addition of an extremely small amount, but if it is less than 0.0005%, its effect is not sufficient, and if it exceeds 0.005%, hardenability is adversely affected. Lower. Therefore, the content is 0.0
It was set to 005 to 0.005%.

Ti: Ti fixes Free-N in the steel, improves the effect of B on the hardenability, and finely precipitates Ti carbide, Ti-containing composite carbide, and Ti nitride during carburization. Is an element necessary for suppressing coarsening of the austenite grain size of
If it is less than 8%, the effect is not sufficient, and if it exceeds 0.2%, the amount of precipitates becomes excessive and the workability deteriorates. Therefore, the content is set to 0.08 to 0.2%.

When N: N is contained in an amount of more than 0.015%, TiN increases, and the fatigue characteristics are adversely affected. Therefore, the content is set to 0.015% or less.

Cr: Cr is an element effective in improving hardenability, toughness, and fatigue life. If it is too small, it has no effect, and if it is too large, the effect is saturated. Therefore, the content is Cr: 0.
15 to 2.0%. .

Al: Al is an element used as a deoxidizing agent, and if it is less than 0.005%, its effect is not sufficient, and if it exceeds 0.05%, alumina-based oxide increases and fatigue characteristics and workability are increased. Lower. Therefore, the content is 0.0
05-0.05%

The production method according to the present invention is intended for the steel according to claim 1 or 2 containing the above-mentioned chemical components, or steel in which any additional element is added to these chemical components,
In order to produce a gear that does not generate mixed particles, the bloom or steel ingot is heated to 1200 ° C, preferably 1250 ° C or higher,
Steel billet rolling-air cooling, heating to 800 to 1050 ° C, rolling of steel rod wire rod, and then reheating to a temperature range of 800 to 1050 ° C in the heat history of a series of gear forming processes including hot forging. Is.

The reason for heating at 1200 ° C., preferably 1250 ° C. or higher, rolling the billet and air-cooling is that Ti carbide, Ti-containing composite carbide, and Ti nitride are solid-solved at the stage before heating during rolling of the steel bar wire rod. This is to keep it. 1200
If the heating temperature is lower than 0 ° C, solid solution of Ti carbide, Ti-containing composite carbide, and Ti nitride is insufficient. Ti carbide, T
A composite carbide containing i, Ti nitride is finely precipitated, heated to 800 to 1050 ° C., rolled into a steel bar wire rod, and further processed into a series of gears including hot forging. By heating to 1050 ° C., hot forging, and then cold forging, a gear that does not generate mixed particles during carburization is manufactured.

If the heating temperature at the time of rolling the bar steel wire rod or hot forging exceeds 1050 ° C., the growth of fine precipitates occurs, and the austenite grain size characteristics at the time of carburizing are deteriorated. At 1200 ° C or higher, the particle size characteristics are restored,
After rolling and forging of steel bar wire rods, a bainite structure is easily formed and workability is deteriorated. Therefore, the heating temperature at the time of hot bar forging at the time of rolling a steel bar wire rod was set to 800 to 1050 ° C.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described through the following examples. First, the steel composition in the embodiment and the steel composition in the comparative example are shown in Table 1. 1-No.
6 shows.

[0020]

[Table 1]

No. 1, No. 2, No. No. 3 is steel in the present invention, No. 3 4, No. 5, No. 6 is SCM steel (Ti: unavoidable impurity amount, B: none) in the comparative example. No. 1, No. 2, No. Mo in 3 is contained as an unavoidable impurity. Using these blooms or steel ingots, billets are rolled at a temperature of 1250 ° C., air-cooled, extracted at 1050 ° C. in a heating furnace, and rolled into bar steel wire under the condition that the rolling ends at 950 ° C. The gear was reheated and hot forged to investigate whether or not mixed particles were generated. The hot forging heating temperature during gear processing is shown in Table 2 of the example.
Shown in.

[0022]

EXAMPLE A case-hardening steel having the chemical composition shown in Table 1 was melted in an electric melting furnace, heated to 1250 ° C., billet rolling to air cooling, and extracted at 1050 ° C. in a heating furnace to determine the rolling end temperature. It was rolled at 950 ° C.

[0023]

[Table 2]

After heating it to a temperature shown in Table 2, hot forging was performed, and after tooth cooling and forging, carburizing was performed at 950 ° C., and austenite grain size characteristics were examined. Table 3 shows the results of determining whether or not mixed particles have occurred according to JIS G0551.

[0025]

[Table 3]

No. 3 in Table 3 4, No. 5, No. 6, the SCM steel of the comparative example (Ti: inevitable impurity amount,
In the case of (B: None), mixed particles are generated regardless of the heating temperature during hot heating. On the other hand, the steel of the composition range of the present invention is No. As shown in No. 3, when the heating temperature during hot forging is 1150 ° C., mixed grains are generated, but No. 1
As shown in No. 3, when the heating temperature during hot forging is 900 ° C. and No. As shown in 2, the heating temperature during hot forging is 105
When the temperature was 0 ° C., no mixed grains were generated and excellent crystal grain size characteristics were obtained. As described above, with the steel satisfying the composition range of the present invention, it is possible to manufacture a gear having excellent grain size characteristics by limiting the heating temperature during hot forging.

[0027]

As described above, the gear manufactured by the method of the present invention using the case-hardening boron steel containing Ti and B as a raw material has a compound in which finely precipitated in the steel is austenite during carburization. Excellent properties such as suppressing the growth of crystal grain size, producing no mixed grains, little heat treatment distortion, and less breakage can be obtained.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22C 38/38 C22C 38/38 F term (reference) 3J030 BC02 BC03 BC06 4E087 AA01 BA02 BA17 CB01 DB15 HA01 4K032 AA01 AA02 AA05 AA11 AA12 AA16 AA19 AA21 AA31 AA35 BA02 CA03 CF03

Claims (2)

[Claims] 1. C: 0.10 to 0.25% by mass%
Si: 0.03 to 0.35%, Mn: 2.0% or less, C
r: 0.15-2.00%, B: 0.0005-0.0
05%, Ti: 0.08 to 0.2%, N: 0.015%
Hereinafter, a bloom or steel ingot containing Al: 0.005 to 0.05% and the balance Fe and unavoidable impurities
800 ~ after heating to 200 ℃ or more, rolling billet and air cooling
After heating to 1050 ° C, rolling the steel bar wire rod, and further in the heat history of the process of processing into a series of gears including hot forging, 80
A method for producing a gear having excellent austenite grain size characteristics during carburization, which comprises reheating to a temperature range of 0 to 1050 ° C. 2. C: 0.10 to 0.25% by mass,
Si: 0.03 to 0.35%, Mn: 2.0% or less, C
r: 0.15-2.00%, B: 0.0005-0.0
05%, Ti: 0.08 to 0.2%, N: 0.015%
Hereinafter, Al: 0.005 to 0.05% and Mo: 0.
A bloom or steel ingot containing 03 to 1.0% and the balance consisting of Fe and unavoidable impurities is heated to 1200 ° C. or higher, rolled into a billet, air-cooled, and heated to 800 to 1050 ° C., and then rolled into a steel bar wire rod. And a method of manufacturing a gear having excellent austenite grain size characteristics during carburization, which comprises reheating to a temperature range of 800 to 1050 ° C. in a heat history of a series of gear processing steps including hot forging. .